Flat heat pipe

ABSTRACT

An exemplary flat heat pipe with an evaporator section and a condenser section includes a casing, and a first wick structure and a second wick structure in the casing. The casing defines a first vapor channel within the evaporator section. The first wick structure contacts an inner surface of the casing at the condenser section. The first wick structure includes a contact portion in contact with the inner surface of the casing, and an isolated portion from the inner surface of the casing. The isolated portion and the inner surface of the casing cooperatively define therebetween a second vapor channel in communication with the first vapor channel. The second wick structure contacts the inner surface of the casing at the evaporator section. The second wick structure joins the first wick structure at a joint between the evaporator section and the condenser section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to two co-pending applications respectively entitled “FLAT HEAT PIPE AND METHOD FOR MANUFACTURING THE SAME” (attorney docket number US31525) and “FLAT HEAT PIPE WITH VAPOR CHANNEL” (attorney docket number US32037), assigned to the same assignee of this application and filed on the same date as this application. The two related applications are incorporated herein by reference.

BACKGROUND

1. Technical Field

The disclosure generally relates to heat transfer apparatuses, and particularly to a heat pipe with high heat transfer efficiency.

2. Description of Related Art

Heat pipes are widely used in various fields for heat dissipation purposes due to their excellent heat transfer performance. One commonly used heat pipe includes a sealed tube made of heat conductive material, with a working fluid contained therein. The working fluid conveys heat from one end of the tube, typically referred to as an evaporator section, to the other end of the tube, typically referred to as a condenser section. Preferably, a wick structure is provided inside the heat pipe, lining an inner wall of the tube, and drawing the working fluid back to the evaporator section after it condenses at the condenser section.

During operation, the evaporator section of the heat pipe maintains thermal contact with a heat-generating electronic component. The working fluid at the evaporator section absorbs heat generated by the electronic component, and thereby turns to vapor. Due to the difference in vapor pressure between the two sections of the heat pipe, the generated vapor moves, carrying the heat with it, toward the condenser section. At the condenser section, the vapor condenses after transferring the heat to, for example, fins thermally contacting the condenser section. The fins then release the heat into the ambient environment. Due to the difference in capillary pressure which develops in the wick structure between the two sections, the condensate is then drawn back by the wick structure to the evaporator section where it is again available for evaporation.

In ordinary use, the heat pipe is flattened to increase a contact area with the electronic component and enable smaller electronic products to incorporate the heat pipe. However, this may downsize a vapor channel of the heat pipe through which the vapor flows from the evaporator section to the condenser section. In such case, the generated vapor may not move toward the condenser section in a timely manner, and the heat transfer efficiency of the heat pipe is thereby reduced.

What is needed, therefore, is a flat heat pipe which can overcome the described limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the various views, and all the views are schematic.

FIG. 1 is an abbreviated, lateral side plan view of a heat pipe in accordance with a first embodiment of the disclosure.

FIG. 2 is an enlarged, transverse cross section of the heat pipe of FIG. 1, taken along line II-II thereof.

FIG. 3 is an enlarged, transverse cross section of the heat pipe of FIG. 1, taken along line thereof.

FIG. 4 is an enlarged, longitudinal cross section of the heat pipe of FIG. 1, taken along line IV-IV thereof.

FIG. 5 is similar to FIG. 3, but shows a transverse cross section of a heat pipe according to a second embodiment of the disclosure.

FIG. 6 is similar to FIG. 3, but shows a transverse cross section of a heat pipe according to a third embodiment of the disclosure.

FIG. 7 is similar to FIG. 2, but shows a transverse cross section of a heat pipe according to a fourth embodiment of the disclosure.

DETAILED DESCRIPTION

Referring to FIGS. 1-3, a heat pipe 10 in accordance with a first embodiment of the disclosure is shown. The heat pipe 10 is a flat heat pipe, and includes a flat tube-like casing 11 with two ends thereof sealed, and a variety of elements enclosed in the casing 11. Such elements include two first wick structures 12, 13, a second wick structure 14, and a working medium (not shown).

The casing 11 is made of metal or metal alloy with a high heat conductivity coefficient, such as copper, copper-alloy, or other suitable material. The casing 11 is elongated, and has an evaporator section 111 and an opposite condenser section 113 located end-to-end along a longitudinal direction thereof. The casing 11 has a width larger than its height. In particular, the casing 11 has a flattened transverse cross section. To meet the height requirements of common electronic products, the height of the casing 11 is preferably less than 2 millimeters (mm). The casing 11 is hollow, and includes a top plate 114, a bottom plate 115 opposite to the top plate 114, and two side plates 116, 117 interconnecting the top and bottom plates 114, 115. The top and bottom plates 114, 115 are flat and parallel to each other. The side plates 116, 117 are arcuate and respectively disposed at opposite lateral sides of the casing 11. The casing 11 defines a first vapor channel 141 within the evaporator section 111.

The second wick structure 14 is made of sintered metal powder, such as copper powder or other suitable material. The second wick structure 14 is only located in the evaporator section 111, and sandwiched between the top and bottom plates 114, 115 of the casing 11. In this embodiment, the second wick structure 14 is annular, and snugly contacts an entire inner surface of the casing 11 at the evaporator section 111. The first vapor channel 141 is defined in the second wick structure 14.

Each of the first wick structures 12, 13 is an elongated hollow tube, and extends longitudinally from a joint 149 located between the evaporator section 111 and the condenser section 113 into and through an entire length of the condenser section 113. An inner space 140 is longitudinally defined in each of the first wick structures 12, 13. Each of the first wick structures 12, 13 is a monolayer-type structure formed by weaving a plurality of metal wires such as copper or stainless steel wires. The first wick structures 12, 13 thus have a plurality of pores therein. Alternatively, each of the first wick structures 12, 13 can be a multilayer-type structure layered along a radial direction thereof by weaving a plurality of metal wires.

The first wick structures 12, 13 are only located in the condenser section 113. In this embodiment, the first wick structures 12, 13 are disposed at opposite inner sides of the casing 11, respectively. Each of the first wick structures 12, 13 is extruded to a flattened shape by the inner surface of the casing 11. Each first wick structure 12, 13 has a flattened transverse cross section, similar in principle to the flattened transverse cross section of the casing 11. In particular, each first wick structure 12, 13 includes a top wall 121, 131, a bottom wall 122, 132 opposite to the top wall 121, 131, and a left sidewall 123, 133 and a right sidewall 124, 134 interconnecting the top and bottom walls 121, 131, 122, 132. The top and bottom walls 121, 131, 122, 132 are flat and parallel to each other. The left and right sidewalls 123, 133, 124, 134 are arcuate and respectively disposed at opposite lateral sides of each first wick structure 12, 13.

The first wick structure 12 is disposed at a right inner side of the casing 11 within the condenser section 113. The top wall 121, the bottom wall 122 and the right sidewall 124 of the first wick structure 12 cooperatively form a U-shaped contact portion in contact with an inner surface of the casing 11. In particular, the contacting inner surface of the casing 11 includes the side plate 116, and a portion of each of the top and bottom plates 114, 115 adjacent to the side plate 116. The left sidewall 123 of the first wick structure 12 forms a C-shaped isolated portion 126 isolated from the inner surface of the casing 11.

The first wick structure 13 is disposed at a left inner side of the casing 11 within the condenser section 113. The top wall 131, the bottom wall 132 and the left sidewall 133 of the first wick structure 13 cooperatively form a U-shaped contact portion in contact with an inner surface of the casing 11. In particular, the contacting inner surface of the casing 11 includes the side plate 117, and a portion of each of the top and bottom plates 114, 115 adjacent to the side plate 117. The right sidewall 134 of the first wick structure 13 forms a C-shaped isolated portion 136 isolated from the inner surface of the casing 11. The left sidewall 123 of the first wick structure 12, the right sidewall 134 of the first wick structure 13 and the inner surface of the casing 11 cooperatively define a second vapor channel 142 therebetween. In other words, the isolated portions 126, 136 and the inner surface of the casing 11 cooperatively define the second vapor channel 142 therebetween. An end of the second vapor channel 142 communicates with an end of the first vapor channel 141. The first and second vapor channels 141, 142 cooperatively provide a passage through which the vapor flows from the evaporator section 111 to the condenser section 113. The isolated portions 126, 136 of the first wick structures 12, 13 face a center of the casing 11.

Referring also to FIG. 4, the first wick structures 12, 13 extend longitudinally in the condenser section 113 to the second wick structure 14, and join the second wick structure 14 at the joint 149 between the evaporator section 111 and the condenser section 113 via sintering. The first and second wick structures 12, 13, 14 cooperatively form a composite wick structure 17 in the casing 11. A diameter of the inner space 140 of each first wick structure 12, 13 exceeds a thickness of a circumferential wall of the second wick structure 14 as measured in a horizontal direction of the casing 11. The second wick structure 14 blocks a portion of the end of the inner space 140 of each first wick structure 12, 13 at the joint 149. The inner spaces 140 of the first wick structures 12, 13 and the second vapor channel 142 between the first wick structures 12, 13 all communicate with the first vapor channel 141.

The working medium is saturated in the first and second wick structures 12, 13, 14. The working medium is usually selected from a liquid such as water, methanol, or alcohol, which has a low boiling point. The casing 11 of the heat pipe 10 is evacuated and hermetically sealed after the working medium is injected into the casing 11 and saturated in the first and second wick structures 12, 13, 14. Thus, the working medium can easily evaporate when it receives heat at the evaporator section 111 of the heat pipe 10.

In operation, the evaporator section 111 of the heat pipe 10 is placed in thermal contact with a heat source (not shown) that needs to be cooled. The heat source can, for example, be a central processing unit (CPU) of a computer. The working medium contained in the evaporator section 111 of the heat pipe 10 is vaporized when receiving heat generated by the heat source. The generated vapor moves from the evaporator section 111 via the vapor channels 141, 142 to the condenser section 113. After the vapor releases its heat and condenses in the condenser section 113, the condensate is returned by the first and second wick structures 12, 13, 14 to the evaporator section 111 of the heat pipe 10, where the condensate is again available for evaporation.

In the heat pipe 10, the first and second wick structures 12, 13, 14 cooperatively form the composite wick structure 17 in the casing 11. This increases capillary force, and reduces flow resistance and heat resistance. As a result, the condensate is returned to the evaporator section 111 of the heat pipe 10 rapidly, thus preventing potential drying out at the evaporator section 111. In addition, the first and second wick structures 12, 13, 14 are only located in the condenser section 113 and the evaporator section 111, respectively. This enlarges the first and second vapor channels 141, 142 in the evaporator and condenser sections section 111, 113, and further promotes the flow of the working medium in the heat pipe 10. Furthermore, the first wick structures 12, 13 are joined to the second wick structure 14 at the joint 149 via sintering. Thus, the first wick structures 12, 13 closely and continuously connect with the second wick structure 14, and the working medium can be rapidly saturated in the second wick structure 14 after returning to the evaporator section 111 via the first wick structures 12, 13. Additionally, the first wick structures 12, 13 cannot move freely in the casing 11. This increases the flow of the working media in the casing 11, and improves the heat transfer performance of the heat pipe 10.

Referring to FIG. 5, a heat pipe 20 in accordance with a second embodiment of the disclosure is shown. The heat pipe 20 differs from the heat pipe 10 of the first embodiment only in that there is only one first wick structure 22. The first wick structure 22 is disposed in a center of the casing 11 within the condenser section 213.

At the condenser section 213 of the heat pipe 20, top and bottom walls 221, 222 of the first wick structure 22 form two contact portions in contact with the inner surface of the casing 11, respectively. In particular, the contacting inner surface of the casing 11 includes the top and bottom plates 114, 115. Two sidewalls 223, 224 of the first wick structure 22 form two isolated portions isolated from the inner surface of the casing 11, respectively. Two passages 2421, 2422 are respectively defined between the sidewalls 223, 224 of the first wick structure 22 and the inner surface of the casing 11, the passages 2421, 2422 being disposed beside opposite sides of the first wick structure 22, respectively. The two passages 2421, 2422 cooperatively form a second vapor channel 242. Ends of the passages 2421, 2422 communicate with an end of the first vapor channel 141 of the second wick structure 14.

Referring to FIG. 6, a heat pipe 30 in accordance with a third embodiment of the disclosure is shown. The heat pipe 30 differs from the heat pipe 10 of the first embodiment only in that another first wick structure 35 is deployed in a center of the casing 11, for a total of three first wick structures 12, 13, 35. The first wick structures 12, 13, 35 are spaced from each other. The first wick structure 35 is the same as the first wick structure 22 of the second embodiment.

At the condenser section 313 of the heat pipe 30, the right sidewall 134 of the first wick structure 13, the left sidewall 353 of the first wick structure 35, and the inner surface of the casing 11 cooperatively define a passage 3421 therebetween. The left sidewall 123 of the first wick structure 12, the right sidewall 354 of the first wick structure 35, and the inner surface of the casing 11 cooperatively define another passage 3422 therebetween. The two passages 3421, 3422 cooperatively form a second vapor channel 342. Ends of the passages 3421, 3422 communicate with an end of the first vapor channel 141 of the second wick structure 14.

Referring to FIG. 7, a heat pipe 40 in accordance with a third embodiment of the disclosure is shown. The heat pipe 40 differs from the heat pipe 10 of the first embodiment only in that a second wick structure 44 contacts a portion of the inner surface of the casing 11 at the evaporator section 411 which corresponds to an area of an outside of the casing 11 designated for contacting a heat-generating electronic component 70. In particular, the second wick structure 44 is plate-shaped, and contacts an inner surface of the bottom plate 115 of the casing 11. The electronic component 70 contacts an outer surface of the bottom plate 115. The second wick structure 44 and the inner surface of the casing 11 cooperatively define a first vapor channel 441 therebetween. More particularly, the second wick structure 44, the top plate 114 and the side plates 116, 117 cooperatively define the first vapor channel 441 therebetween.

In the heat pipe 40, the second wick structure 44 contacts a portion of the casing 11 within the evaporator section 411 corresponding to the electronic component 70. This enlarges the first vapor channel 441 in the evaporator section 411, and further promotes the flow of the working medium in the heat pipe 40. In addition, heat generated by the electronic component 70 can be rapidly transferred to the second wick structure 44 by the casing 11, whereby the heat transfer performance of the heat pipe 40 is improved.

It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A flat heat pipe with an evaporator section and a condenser section at opposite ends thereof, the flat heat pipe comprising: a hollow flat casing defining a first vapor channel within the evaporator section; a first wick structure received in the casing at the condenser section, the first wick structure in contact with an inner surface of the casing at the condenser section, the first wick structure comprising at least one contact portion in contact with the inner surface of the casing, and at least one isolated portion isolated from the inner surface of the casing, the at least one isolated portion and the inner surface of the casing cooperatively defining a second vapor channel therebetween, the first and second vapor channels in communication with each other; and a second wick structure received in the casing at the evaporator section, the second wick structure in contact with an inner surface of the casing at the evaporator section, the second wick structure joining the first wick structure at a joint between the evaporator section and the condenser section.
 2. The flat heat pipe of claim 1, wherein the first wick structure is formed by weaving a plurality of metal wires, the second wick structure is made of sintered metal powder, and the first and second wick structures are joined together by sintering.
 3. The flat heat pipe of claim 2, wherein the first wick structure is a hollow tube, and comprises a top wall, a bottom wall opposite to the top wall, and a first sidewall and a second sidewall interconnecting the top and bottom walls, the first wick structure is located in the center of the casing, and the second vapor channel comprises two passages respectively defined between the sidewalls of the first wick structure and the inner surface of the casing.
 4. The flat heat pipe of claim 3, wherein the at least one contact portion comprises two contact portions, the at least one isolated portion comprises two isolated portions, the top and bottom walls of the first wick structure form the two contact portions in contact with the inner surface of the casing, respectively, and the first and second sidewalls of the first wick structure form the two isolated portions isolated from the inner surface of the casing.
 5. The flat heat pipe of claim 2, further comprising another first wick structure received in the casing at the condenser section, wherein the casing comprises opposite top and bottom plates, and two opposite side plates between the top and bottom plates, the two first wick structures are disposed at opposite inner sides of the casing at the side plates, respectively, each of the two first wick structures comprises a top wall, a bottom wall opposite to the top wall, and a first sidewall and a second sidewall interconnecting the top and bottom walls, the first sidewalls of the first wick structures faces each other, and the second vapor channel is defined between the first sidewalls of the first wick structures and the inner surface of the casing.
 6. The flat heat pipe of claim 5, wherein the at least one contact portion comprises two contact portions, the at least one isolated portion comprises two isolated portions, the top wall, the bottom wall and the first sidewall of each first wick structure cooperatively form one of the contact portions in contact with the inner surface of the casing, and the second sidewall of each first wick structure forms one of the isolated portions isolated from the inner surface of the casing.
 7. The flat heat pipe of claim 2, further comprising another two first wick structures, wherein the casing comprises opposite top and bottom plates, and two opposite side plates between the top and bottom plates, the three first wick structures are spaced from each other, two of the first wick structures are disposed at opposite inner sides of the casing at the side plates, respectively, and the other first wick structure is located in the center of the casing, each of the first wick structures comprises a top wall, a bottom wall opposite to the top wall, and a first sidewall and a second sidewall interconnecting the top and bottom walls, the second vapor channel comprises two passages, one of the passages is defined between the second sidewall of the first wick structure at one of the side plates of the casing, the first sidewall of the first wick structure in the center of the casing and the inner surface of the casing, and the other passage is defined between the second sidewall of the first wick structure at the other side plate of the casing, the second sidewall of the first wick structure in the center of the casing and the inner surface of the casing.
 8. The flat heat pipe of claim 7, wherein the at least one contact portion comprises four contact portions, the at least one isolated portion comprises four isolated portions, the top wall, the bottom wall and the first sidewall of each of the first wick structures at the opposite side plates of the casing cooperatively form two of the contact portions in contact with the inner surface of the casing, the top and bottom walls of the first wick structure in the center of the casing form another two of the contact portions in contact with the inner surface of the casing, respectively, the second sidewall of each of the first wick structures at the opposite side plates of the casing form two of the isolated portions isolated from the inner surface of the casing, and the first and second sidewalls of the first wick structure in the center of the casing form another two of the isolated portions isolated from the inner surface of the casing, respectively.
 9. The flat heat pipe of claim 1, wherein the second wick structure contacts a portion of the inner surface of the casing at the evaporator section which corresponds to an area of an outside of the casing designated for contacting a heat-generating electronic component.
 10. The flat heat pipe of claim 1, wherein the first wick structure is an extruded flattened shape.
 11. The flat heat pipe of claim 1, wherein a height of the casing is less than 2 millimeters.
 12. The flat heat pipe of claim 1, wherein the first wick structure is a hollow tube, and defines an inner space therein, and the inner space communicates with the first vapor channel.
 13. The flat heat pipe of claim 12, wherein the second wick structure blocks a portion of an end of the inner space of the first wick structures at the joint.
 14. A flat heat pipe with an evaporator section and a condenser section at opposite ends thereof, the flat heat pipe comprising: a hollow flat casing defining a first vapor channel within the evaporator section; a first wick structure received in the casing at the condenser section, the first wick structure formed by weaving a plurality of metal wires, the first wick structure comprising at least one isolated portion isolated from an inner surface of the casing, the at least one isolated portion and the inner surface of the casing cooperatively defining a second vapor channel therebetween, the first and second vapor channels in communication with each other; and a second wick structure received in the casing at the evaporator section, the second wick structure made of sintered metal powder, the second wick structure joining the first wick structure at a joint between the evaporator section and the condenser section.
 15. The flat heat pipe of claim 14, wherein the first and second wick structures are joined together by sintering.
 16. The flat heat pipe of claim 14, wherein the first wick structure is a hollow tube, and comprises a top wall, a bottom wall opposite to the top wall, and a first sidewall and a second sidewall interconnecting the top and bottom walls, the first wick structure is located in the center of the casing, and the second vapor channel comprises two passages defined between the sidewalls of the first wick structure and the inner surface of the casing, respectively.
 17. The flat heat pipe of claim 14, further comprising another first wick structure, wherein the casing comprises opposite top and bottom plates, and two opposite side plates between the top and bottom plates, the two first wick structures are disposed at the opposite side plates of the casing, respectively, each of the two first wick structures comprises a top wall, a bottom wall opposite to the top wall, and a first sidewall and a second sidewall interconnecting the top and bottom walls, the first sidewalls of the first wick structures face each other, and the second vapor channel is defined between the first sidewalls of the first wick structures and the inner surface of the casing.
 18. The flat heat pipe of claim 14, further comprising another two first wick structures, wherein the casing comprises opposite top and bottom plates, and two opposite side plates between the top and bottom plates, the three first wick structures are spaced from each other, two of the first wick structures are disposed at opposite side plates of the casing, respectively, the other first wick structure is located in the center of the casing, each of the first wick structures comprises a top wall, a bottom wall opposite to the top wall, and a first sidewall and a second sidewall interconnecting the top and bottom walls, the second vapor channel comprises two passages, one of the passages is defined between the second sidewall of the first wick structure at one of the side plates of the casing, the first sidewall of the first wick structure in the center of the casing and the inner surface of the casing, and the other passage is defined between the second sidewall of the first wick structure at the other side plate of the casing, the second sidewall of the first wick structure in the center of the casing and the inner surface of the casing.
 19. The flat heat pipe of claim 14, wherein the second wick structure contacts a portion of the inner surface of the casing at the evaporator section which corresponds to an area of an outside of the casing designated for contacting a heat-generating electronic component.
 20. The flat heat pipe of claim 14, wherein the first wick structure is a hollow tube, and defines an inner space therein, the second wick structure blocks a portion of an end of the inner space of the first wick structure at the joint, and the inner space of the first wick structure communicates with the first vapor channel. 